Visual Basic 6 Programming

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					             Visual Basic 6
             Programming.
                Lecture 1 : January 2005
                Dr. Andrew Paul Myers



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             Course Methods.
                Lectures.
                Handout notes.
                Supervised practical work.
                Weekly submission of exercises.
                Weekly feedback on exercises.
                Model Answers.
                Final project : 12.00 Wed. 19th May 2004.
                Clinics for final Project.
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             Introduction.
                A course in Visual Basic 6.
                Why Visual Basic 6 (VB6)?
                Objectives :
                         •   General education in computing.
                         •   Introduction to programming.
                         •   First write a simple program, then…
                         •   Write a more complex program.
                Course Benefits :
                         • I.T. is a part of all our lives and getting more so!
                         • VB6 and computing skills for other courses.
                         • Future employment.

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             Tools For The Job.
                Programming Environment :

                    CFS client PC.
                    Windows 2000.
                    Microsoft Visual Studio 6 SP5.
                    Computers in G73 only at present!




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             Programming
             Languages.
                You are users!
                How computers work.
                Machine code.
                High level languages.
                BASIC : Beginners All purpose Symbolic
                 Instruction Code.
                Other languages :
                       • FORTRAN, C/C++ & Java


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             Programming Cycle.
                Analyse the task.
                Plan the program, a structured approach!
                Flowcharts & Pseudo-code (Week 2).
                Edit your source code.
                Execute and debug program (Week 2)
                Edit source code as necessary.



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              Setting up VB6 on CFS.
             VB6 is part of MS Visual Studio 6.
             Select :
                 Start Menu
                 Programs
                          Installable Software
             Then navigate to :
                 Central Software
                         Programming Languages
             Double click on :
                 Install MS Visual Studio V6 SP5

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             VB6 Help : MSDN.
                Visual Studio 6 has an extensive, inbuilt
                 help system call MSDN. MicroSoft
                 Developer Network.

                Before this can be used select Setup Help
                 for this session in the MS VS6 folder on
                 the Programs menu.

                 Only run this once per login session.

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             Starting VB6.
                After setup a new folder is added to your
                 programs menu.

                Select Microsoft Visual Basic 6 from the MS
                 Visual Studio V6 SP5 folder.

                Tip : Create a short cut on your desktop.

                This will start the VB6 IDE.
                 Integrated Programming Environment.
                 Select Standard EXE as project type.
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             The VB IDE.
                 Has Standard MicroSoft “feel”.
                Title Bar. Status : Design, run, debug.
                Menu Bar. Pull down menus.
                Tool Bar.
                Tool Box. For adding controls.
                Project Explorer. List project modules.
                Properties Window.
                Form Layout.
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             On we go…




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             Structure of VB
             Program.
             VB programs are made up of different
             subroutines (or procedures) of the form:

             Private Sub <name>()
               Comment statement(s)
               Declaration statement(s)
               BASIC statement(s)
             End Sub
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             VB Statements.
                Comments : Used to document programs
                 and make them more readable. USE
                 THEM !!!

                    „ A Comment!

                Terminate a program.

                     End
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               Computers store and add
               numbers (very fast).
              Computer memory is divided into separate sections.
              Each is identified by a number (its address).

             Alan       Bruce        Claire     Dan         Ethel ……..
         A computer language allows us to identify these by names.
         Then to manipulate the numbers in them.



                     Alan = Bruce + Claire
                            An assignment statement.
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      Bits, bytes and nibbles (its half a byte!).
                     8 bits make a byte

                     1 1 1 0 1 0 1 1 1 1 1 0 1 0 1 1

        Each bit can be set to 1 or 0, so within one byte (8 bits) we can
        represent numbers in the range 0 to 255 i.e. 2^8.
       Combining multiple bytes, we can store numbers:

       16 bits = 2 bytes stores 2^16 = 0 to 65535
       32 bits = 4 bytes stores 2^32 = 0 to 4294967295

       These are whole numbers (integers), no decimals allowed.
       We are restricted to numbers +/- 2 billion.
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             Different Forms of Storage.
      A large number on a calculator is represented in exponential (also
       called scientific) format e.g. 1.23456E+23.
      If we take 4 bytes of memory, and store the mantissa (1.23456) in 3
       bytes, and the exponent (+23) in one byte, we can store real
       numbers, with a greater range.
      Represent letters by a numerical code from 0 – 255 (ASCII) and store
       them in one byte. Text can then be stored as a linked set of bytes,
       called a String.

                 0 1 1 0 1 0 1 1 0 0 1 0 1 0 1 1

                   ASCII 107 is k    ASCII 43 is +
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             Types of Variables.
                Integers (whole numbers)
                Real numbers.
                  Single.
                  Double (twice the number of bytes).

                Strings.
                And others coming later…
                Variants.
                  All types automatically converting.
                  DANGEROUS! – Don’t go there!

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             Variable Names.
                 Data is stored as variables, each with a
                 different name. Variable names are:

                Case insensitive.
                Up to 255 characters long.
                First character must be a letter.
                Can use any combination of alphanumeric
                 characters and the underscore character.

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             Examples.
             Value              yes
             3radius            no
             Question&Reply     no
             Density_of_water   yes
             lngRadius1         yes




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             Hungarian Notation.
              A convention of prefixes for variable
              names, depending on variable type.

              String : str           Integer : int
              Long Integer : lng     Single : sng
              Double : dbl           Boolean : bln
              Currency : cur         Variant : vnt


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             Variable Types I
                 VB6 has 14 standard types.

                String : Hold characters, approx 231, can
                 be null (empty). Can be identified by $.

                     strText$=“Hello.”
                     strEmptyText = “”


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             Variable Types II.
                Integer : Range –32,768 to +32,767. Can
                 be identified by %.
                     intValue% = 1
                     intValue2 = 1000

                Long Integer : Larger range (231).
                    lngValue1& = 56000
                    lngValue2 = -56000
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             Variable Types III.
                Single Precision : Real numbers. Accuracy of 7
                 digits.
                      sngReal_Number1! = 1.23
                      sngReal_Number2 = -0.345

                Double Precision : Accuracy of 16 digits
                    dblValue1# = 0.435827348593
                    dblValue2 = 23.4782947373

             Reals are slower than integers in calculations!

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             Variable Types IV.
                Boolean : True or False?

                     blnAnswer = False

                Other types include : Currency, Date, Byte
                 (range 0 to 255) and variant (can be any
                 data type – very flexible, but dangerous!).


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        Variable Type Declarations I
             Declare all variables before use! Good programming practice.
             Also avoids having to use the suffixes $, #, ! etc.

             Use the Dim statement. e.g.

             Dim <variable> as <data type>

             Dim intDays as Integer
             Dim strText as String, dblAns as Double

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   Variable Type Declarations II
             Declaring all variables before use is good programming
             practice. Use the “Option Explicit” command to make VB insist
             of variables being declared before you can use them.

             Option Explicit

             This also avoids having to use the suffixes $, #, ! etc, as all
             variable types are explicitly defined.

             Note : This check is carried out when the program is run, not at
             the editing stage!
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             Assignments I.
                5 basic mathematical operators:
                 Addition (+)       Subtraction (-)
                 Division(/)        Multiplication (*)
                 Exponentiation (^)
                Precedence follows BODMAS.
                Parentheses can be used to over ride
                 precedence.
                     6*5+4*3             gives 42
                     (((6 * 5) + 4) * 3) gives 102

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                    Assignments II.
             <variable> = <value> | <variable> | <expression>

             Examples :

             intValue = 1
             strText2 = strText1
             intValue = intValue + 1
             sngVol = sngLength^3.0
             strText = “Hello”
             dblVol= (4#/3#)*dblPi*dblRadius^3

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              Print Statements.
             Print <expression>

             Print   “Hello!”
             Print   “Value is “; intValue
             Print   “A : “; intA; “ cm.”
             Print   dblRadius


             We shall be using “Text Boxes”!
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             Good Programming
             Style.

                Comment your program!
                Hungarian notation for variable names.
                Use descriptive variable names.
                Blanks lines may be used to improve
                 readability.
                Indent code with “tabs”.


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             References.
             Visual BASIC 6 from the ground up.
             Gary Cornell.
             (Osborne).

             MSDN On-line Help.
             Active subsection :
             Visual Basic Documentation.

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